Glutathione is indicated to be a specific regulator of the activity of a valyl-tRNA synthetase, not replaceable by glutathionyl spermidine or cysteine. The protein complex in which the regulation occurs is suggested to be the 'tip of an iceberg" representing a vast cytoplasmic apparatus that orchestrates protein biosynthesis and cell development. This system could be the seat of function of oncogene proteins that on mutation cause the regulatory malfunctions of cancer.